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<div class="titlepage"><div><div>
<h2 class="title">
<a id="modules-scripting-fields"></a>Accessing document fields and special variables<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/scripting/fields.asciidoc">edit</a>
</h2>
</div></div></div>
<p>Depending on where a script is used, it will have access to certain special
variables and document fields.</p>
<h2>
<a id="_update_scripts"></a>Update scripts<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/scripting/fields.asciidoc">edit</a>
</h2>
<p>A script used in the <a class="xref" href="docs-update.html" title="Update API">update</a>,
<a class="xref" href="docs-update-by-query.html" title="Update by query API">update-by-query</a>, or <a class="xref" href="docs-reindex.html" title="Reindex API">reindex</a>
API will have access to the <code class="literal">ctx</code> variable which exposes:</p>
<div class="informaltable">
<table border="0" cellpadding="4px">
<colgroup>
<col>
<col>
</colgroup>
<tbody valign="top">
<tr>
<td valign="top">
<p>
<code class="literal">ctx._source</code>
</p>
</td>
<td valign="top">
<p>
Access to the document <a class="xref" href="mapping-source-field.html" title="_source field"><code class="literal">_source</code> field</a>.
</p>
</td>
</tr>
<tr>
<td valign="top">
<p>
<code class="literal">ctx.op</code>
</p>
</td>
<td valign="top">
<p>
The operation that should be applied to the document: <code class="literal">index</code> or <code class="literal">delete</code>.
</p>
</td>
</tr>
<tr>
<td valign="top">
<p>
<code class="literal">ctx._index</code> etc
</p>
</td>
<td valign="top">
<p>
Access to <a class="xref" href="mapping-fields.html" title="Meta-Fields">document meta-fields</a>, some of which may be read-only.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<h2>
<a id="_search_and_aggregation_scripts"></a>Search and aggregation scripts<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/scripting/fields.asciidoc">edit</a>
</h2>
<p>With the exception of <a class="xref" href="search-request-body.html#request-body-search-script-fields" title="Script Fields">script fields</a> which are
executed once per search hit, scripts used in search and aggregations will be
executed once for every document which might match a query or an aggregation.
Depending on how many documents you have, this could mean millions or billions
of executions: these scripts need to be fast!</p>
<p>Field values can be accessed from a script using
<a class="xref" href="modules-scripting-fields.html#modules-scripting-doc-vals" title="Doc values">doc-values</a>,
<a class="xref" href="modules-scripting-fields.html#modules-scripting-source" title="The document _source">the <code class="literal">_source</code> field</a>, or
<a class="xref" href="modules-scripting-fields.html#modules-scripting-stored" title="Stored fields">stored fields</a>,
each of which is explained below.</p>
<h3>
<a id="scripting-score"></a>Accessing the score of a document within a script<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/scripting/fields.asciidoc">edit</a>
</h3>
<p>Scripts used in the <a class="xref" href="query-dsl-function-score-query.html" title="Function score query"><code class="literal">function_score</code> query</a>,
in <a class="xref" href="search-request-body.html#request-body-search-sort" title="Sort">script-based sorting</a>, or in
<a class="xref" href="search-aggregations.html" title="Aggregations">aggregations</a> have access to the <code class="literal">_score</code> variable which
represents the current relevance score of a document.</p>
<p>Here’s an example of using a script in a
<a class="xref" href="query-dsl-function-score-query.html" title="Function score query"><code class="literal">function_score</code> query</a> to alter the
relevance <code class="literal">_score</code> of each document:</p>
<div class="pre_wrapper lang-console">
<pre class="programlisting prettyprint lang-console">PUT my_index/_doc/1?refresh
{
  "text": "quick brown fox",
  "popularity": 1
}

PUT my_index/_doc/2?refresh
{
  "text": "quick fox",
  "popularity": 5
}

GET my_index/_search
{
  "query": {
    "function_score": {
      "query": {
        "match": {
          "text": "quick brown fox"
        }
      },
      "script_score": {
        "script": {
          "lang": "expression",
          "source": "_score * doc['popularity']"
        }
      }
    }
  }
}</pre>
</div>
<div class="console_widget" data-snippet="snippets/598.console"></div>
<h3>
<a id="modules-scripting-doc-vals"></a>Doc values<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/scripting/fields.asciidoc">edit</a>
</h3>
<p>By far the fastest most efficient way to access a field value from a
script is to use the <code class="literal">doc['field_name']</code> syntax, which retrieves the field
value from <a class="xref" href="doc-values.html" title="doc_values">doc values</a>. Doc values are a columnar field value
store, enabled by default on all fields except for <a class="xref" href="text.html" title="Text datatype">analyzed <code class="literal">text</code> fields</a>.</p>
<div class="pre_wrapper lang-console">
<pre class="programlisting prettyprint lang-console">PUT my_index/_doc/1?refresh
{
  "cost_price": 100
}

GET my_index/_search
{
  "script_fields": {
    "sales_price": {
      "script": {
        "lang":   "expression",
        "source": "doc['cost_price'] * markup",
        "params": {
          "markup": 0.2
        }
      }
    }
  }
}</pre>
</div>
<div class="console_widget" data-snippet="snippets/599.console"></div>
<p>Doc-values can only return "simple" field values like numbers, dates, geo-
points, terms, etc, or arrays of these values if the field is multi-valued.
It cannot return JSON objects.</p>
<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<h3>Missing fields</h3>
<p>The <code class="literal">doc['field']</code> will throw an error if <code class="literal">field</code> is missing from the mappings.
In <code class="literal">painless</code>, a check can first be done with <code class="literal">doc.containsKey('field')</code> to guard
accessing the <code class="literal">doc</code> map.  Unfortunately, there is no way to check for the
existence of the field in mappings in an <code class="literal">expression</code> script.</p>
</div>
</div>
<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<h3>Doc values and <code class="literal">text</code> fields</h3>
<p>The <code class="literal">doc['field']</code> syntax can also be used for <a class="xref" href="text.html" title="Text datatype">analyzed <code class="literal">text</code> fields</a>
if <a class="xref" href="fielddata.html" title="fielddata"><code class="literal">fielddata</code></a> is enabled, but <span class="strong strong"><strong>BEWARE</strong></span>: enabling fielddata on a
<code class="literal">text</code> field requires loading all of the terms into the JVM heap, which can be
very expensive both in terms of memory and CPU.  It seldom makes sense to
access <code class="literal">text</code> fields from scripts.</p>
</div>
</div>
<h3>
<a id="modules-scripting-source"></a>The document <code class="literal">_source</code><a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/scripting/fields.asciidoc">edit</a>
</h3>
<p>The document <a class="xref" href="mapping-source-field.html" title="_source field"><code class="literal">_source</code></a> can be accessed using the
<code class="literal">_source.field_name</code> syntax. The <code class="literal">_source</code> is loaded as a map-of-maps, so
properties within object fields can be accessed as, for example,
<code class="literal">_source.name.first</code>.</p>
<div class="important admon">
<div class="icon"></div>
<div class="admon_content">
<h3>Prefer doc-values to _source</h3>
<p>Accessing the <code class="literal">_source</code> field is much slower than using doc-values. The
_source field is optimised for returning several fields per result, while doc
values are optimised for accessing the value of a specific field in many
documents.</p>
<p>It makes sense to use <code class="literal">_source</code> when generating a
<a class="xref" href="search-request-body.html#request-body-search-script-fields" title="Script Fields">script field</a> for the top ten hits from a
search result but, for other search and aggregation use cases, always prefer
using doc values.</p>
</div>
</div>
<p>For instance:</p>
<div class="pre_wrapper lang-console">
<pre class="programlisting prettyprint lang-console">PUT my_index
{
  "mappings": {
    "properties": {
      "first_name": {
        "type": "text"
      },
      "last_name": {
        "type": "text"
      }
    }
  }
}

PUT my_index/_doc/1?refresh
{
  "first_name": "Barry",
  "last_name": "White"
}

GET my_index/_search
{
  "script_fields": {
    "full_name": {
      "script": {
        "lang": "painless",
        "source": "params._source.first_name + ' ' + params._source.last_name"
      }
    }
  }
}</pre>
</div>
<div class="console_widget" data-snippet="snippets/600.console"></div>
<h3>
<a id="modules-scripting-stored"></a>Stored fields<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/scripting/fields.asciidoc">edit</a>
</h3>
<p><em>Stored fields</em> — fields explicitly marked as
<a class="xref" href="mapping-store.html" title="store"><code class="literal">"store": true</code></a> in the mapping — can be accessed using the
<code class="literal">_fields['field_name'].value</code> or <code class="literal">_fields['field_name']</code> syntax:</p>
<div class="pre_wrapper lang-console">
<pre class="programlisting prettyprint lang-console">PUT my_index
{
  "mappings": {
    "properties": {
      "full_name": {
        "type": "text",
        "store": true
      },
      "title": {
        "type": "text",
        "store": true
      }
    }
  }
}

PUT my_index/_doc/1?refresh
{
  "full_name": "Alice Ball",
  "title": "Professor"
}

GET my_index/_search
{
  "script_fields": {
    "name_with_title": {
      "script": {
        "lang": "painless",
        "source": "params._fields['title'].value + ' ' + params._fields['full_name'].value"
      }
    }
  }
}</pre>
</div>
<div class="console_widget" data-snippet="snippets/601.console"></div>
<div class="tip admon">
<div class="icon"></div>
<div class="admon_content">
<h3>Stored vs <code class="literal">_source</code>
</h3>
<p>The <code class="literal">_source</code> field is just a special stored field, so the performance is
similar to that of other stored fields.  The <code class="literal">_source</code> provides access to the
original document body that was indexed (including the ability to distinguish
<code class="literal">null</code> values from empty fields, single-value arrays from plain scalars, etc).</p>
<p>The only time it really makes sense to use stored fields instead of the
<code class="literal">_source</code> field is when the <code class="literal">_source</code> is very large and it is less costly to
access a few small stored fields instead of the entire <code class="literal">_source</code>.</p>
</div>
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